In FIGS. 1 and 2, a prior art mechanical joint 10 involves a rotating base 12 and an arm 14 that is hinged to components 16 and 18, which are attached to base 12. Three dimensional movement is enabled by using two independent motions. One motion causes the base 12 to rotate, while of the other motion adjusts the elevation of arm 14. Joint 10 has several limitations in motion. For example, in FIG. 2, arm 14 is positioned in an orientation that is perpendicular to base 12. When joint 10 is in this position, arm 14 is limited to directions 20 and 22. To lay arm 14 along a different direction, for example 24 and 26, joint 10 needs to rotate base 12 first, in order to prepare to lower arm 14. The alternative method is to rotate base 12 and lower arm 14 simultaneously, using a curved path. If particular tasks require path 28 or similar paths, it is extremely cumbersome to employ joint 10. Also, the construction of joint 10 does not support the spinning movement of arm 14 in most positions except for that shown in FIG. 2.
FIG. 3 shows a universal joint 30 constructed in accordance with the prior art. Universal joint 30 includes two shafts 32, 34 connected by a pair of orthogonally oriented hinges 36, 38, respectively. Hinges 36, 38 are attached to each other at their axles 36a, 38a. 